Sleep-state for mobile terminal and service initiation for mobile terminals in sleep-state

ABSTRACT

The invention relates to the initiation of a service to a mobile terminal capable of communicating via at least a first and second access network. Further, the invention relates to a reduction of power consumption of mobile terminals supporting connectivity to at least two access networks. The invention also relates to mobile communication systems and in particular to mobile communications through heterogeneous access networks. In order to prove improved method for initiating services to mobile terminals and/or to reduce power consumption of mobile terminals, the invention introduces of a sleep state that can be entered by the terminal for an access system if same is not used. Upon requesting a service from/to the mobile terminal, the mobile terminal starts service initiation through a second access system and transits back to active state for the first access system for service provision.

FIELD OF THE INVENTION

The invention relates to the initiation of a service to a mobileterminal capable of communicating via at least a first and second accessnetwork. Further, the invention relates to a reduction of powerconsumption of mobile terminals supporting connectivity to at least twoaccess networks. The invention also relates to mobile communicationsystems and in particular to mobile communications through heterogeneousaccess networks.

TECHNICAL BACKGROUND

In 3GPP the evolution of the UMTS architecture is discussed in 3GPP TR23.882, “3GPP System Architecture Evolution: Report on Technical Optionsand Conclusions”, V. 1.0.0 (available at http://www.3gpp.org),incorporated herein by reference. The motivation for the evolutionis—among others—the development of a new air interface and the supportfor mobility between heterogeneous access networks.

An exemplary logical high-level architecture for the evolved system isshown in FIG. 1 and comprises at first an Inter Access System Anchor(Inter AS Anchor), being a user plane anchor for mobility betweendifferent access systems and supporting handover between differentaccess systems. Functions of the anchor are, e.g.

-   -   Packet routing and forwarding,    -   Authentication, authorization and key management,    -   Policy and Charging Enforcement Function,    -   Gateway to PDNs, including IP address allocation from PDN        address space

Furthermore the architecture comprises a Mobility Management Entity(MME) and User Plane Entity (UPE). The functions of the MME are, e.g.,

-   -   Management and storage of UE control plane context,    -   Mobility management,    -   Authentication, authorization and key management,    -   Ciphering/integrity termination for signaling,    -   Management and allocation of temporary user identities,        and the functions of the UPE are, e.g.,    -   Management and storage of UE user plane context    -   Packet routing and forwarding,    -   Policy and Charging Enforcement Function,    -   Ciphering termination for user plane traffic,    -   Trigger/initiation of paging when downlink data arrive for the        UE in idle state.

The MME, UPE and Inter AS Anchor are logical entities, i.e., thefunctionalities can be, e.g., deployed in different physical entities orcombined in one single physical entity. Furthermore it is possible tohave multiple MMEs, UPEs or anchors within one operator domain. Thus,with multiple MMEs/UPEs the data packet route from the anchor to the UEcan be optimized, or the load can be shared between different MMEs/UPEs.In addition the network can provide connectivity to different PDNs(Packet Data Networks) over one or multiple Inter AS Anchors in theoperator domain.

In the evolved system, the terminal (UE) must be registered (attached)with the network to receive services that require registration. Duringthe first registration with the network, a Default IP Access Service isestablished, the UE is provided with an IP address and a default context(comprising e.g., UE/user identities, mobility state, tracking area,security parameters, QoS information, internal routing information andother parameters) is established in the network.

Further, in order to be able to send and receive user data, the UE mustbe in an active state with the 3GPP interface. In this state a radioconnection is established and the UE reports measurements andrequirements to the base station. Then, bearers are established betweenthe UE and the network, carrying first the signaling and later the userdata.

During mobility in active state the UE continuously measures the signalstrength of neighbouring cells and sends measurement reports to thenetwork. When the network decides to use a new base station, itestablishes a new radio link and triggers the UE to handover to the newbase station.

In addition to the active state a mode with lower power consumption issupported. This mode is called idle state and is used when no user datais sent or received. In idle state the cell reselection is performed bythe UE and only tracking area (TA) changes are registered with thenetwork (i.e., not every cell change is reported to the network). Thenetwork does not know the actual location of the UE on cell-level, butonly on TA-level. In idle state UE related contexts are deleted in the3GPP radio access network (RAN) and it is possible to page the UE.

For the sake of completeness the state where the location of the UE inthe 3GPP radio coverage is not known by the network at all (e.g., the UEis switched off) is the detached state.

In case a service requested by the terminal requires a specific QoS,which cannot be provided by the Default IP Access Service, additionalbearer services are required. For this purpose, either the UE or thenetwork requests additional resources. For example, in case of IMSservices (see 3GPP TS 23.228, “IP Multimedia Subsystem (IMS), Stage 2”,V. 7.2.0, available at http://www.3gpp.org, incorporated herein byreference), QoS requirements are signaled during application signaling,the Policy and Charging Rules Function (PCRF—see 3GPP TS 23.203, “Policyand charging control architecture”, V. 0.4.0, available athttp://www.3gpp.org, incorporated herein by reference) authorizes theQoS and triggers the resource establishment. At the MME/UPE the UE'ssubscription is checked, admission control is performed and the resourceestablishment is initiated towards the RAN.

As mentioned above, the evolved system supports access to 3GPP servicesfrom non-3GPP radio access technologies as well. For this purpose eitherthe Inter AS Anchor provides an IP interface and a UE can connect from anon-3GPP access system to the anchor directly via the IP interface, oranother gateway provides the IP interface the UE is connected to, andthe gateway is further connected to the Inter AS Anchor. Because of theIP connectivity between the UE and the gateway/anchor over a non-3GPPnetwork, the connection is connectionless and unreliable. Thus, theInter AS Anchor is not aware whether the UE is reachable or not.

For mobility between 3GPP and non-3GPP radio access technologies a UEwith multimode capabilities is required. When the UE performs a handoverfrom 3GPP to non-3GPP, the Inter AS anchor is informed about thelocation of the UE (e.g., in form of an IP address assigned to theterminal in the non-3GPP network or in form of another identifier of atunnel endpoint the terminal is connected to). In addition to thelocation information the Inter AS anchor is provided with informationabout the user data packets (e.g., IP flows or packets marked withspecific DiffSery Codepoint) to be transferred to the UE over thenon-3GPP network.

The decision, which user data packets can be transferred over thenon-3GPP network may e.g., depend on user subscription or operatorpolicies. For example, for Voice over IMS (VoIMS) low delay is the mainQoS requirement. The connection to a non-3GPP radio access technologymay however provide high data throughput but with highly variable delay.Thus this connection should not be used for the VoIMS service. In casethe operator employs different Inter AS Anchors for different services(e.g., one Inter AS Anchor for IMS services and another Inter AS Anchorfor Internet services), one Inter AS Anchor might not provide theservice for non-3GPP radio access technologies and thus not supportmobility to non-3GPP (see Inter AS Anchor 1 in FIG. 2).

In one exemplary scenario a multimode UE has a non-3GPP and a 3GPPnetwork interface and has an activate connection over the non-3GPP radioaccess technology. Furthermore, the UE wants to receive a service whereeither policies forbid to use the non-3GPP radio access technology orQoS requirements cannot be met in the non-3GPP radio access technology.Hence, the 3GPP network interface must be used for this service.

For being able to receive the 3GPP service over the 3GPP network, the UEmust be either in active or in idle state. In the former case, theservice activation and service delivery can start immediately. In thelatter case, the UE is listening to paging messages and can set up abearer after being paged. However in either states, the powerconsumption of the UE is significantly increased, because the 3GPPinterface is active even when only the non-3GPP interface is used.

A work-around considered in an exemplary embodiment of the invention isto deactivate the 3GPP interface of the UE (i.e., the UE is detached)and to trigger the activation of the 3GPP interface over the non-3GPPnetwork connection. Then, when the 3GPP interface is activated,resources can be set up and the application can be used. But with thissolution the problem arises that the service activation is delayed untilthe connection with the selected 3GPP access network is completelyestablished.

Hence, another potential problem is support of fast establishment forincoming connections over the 3GPP radio access and to enable low powerconsumption for multimode UEs at the same.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved method forinitiating services to mobile terminals and/or to reduce powerconsumption of mobile terminals.

The object is solved by the subject matter of the independent claims.Advantageous embodiments of the invention are subject matters to thedependent claims.

One main aspect of the invention is the introduction of a new statecalled sleep state to reduce the power consumption. In one exemplaryembodiment of the invention, the interface of a mobile terminal to afirst access network is powered off (similar to detached state) toreduce power consumption but some context information of the mobileterminal is still stored in the network (similar to idle) to speed upservice activation at later time.

One embodiment of the invention related to a method for initiating aservice to a mobile terminal capable of communicating via at least afirst and second access network. The mobile terminal has IP connectivityto the first access network and is in a sleep state in the second accessnetwork. For example, at least one of these two access networks may be aradio access network, such as a 3GPP-based (e.g., E-UTRAN, HSPA, UTRAN,etc.) or non-3GPP-based (e.g., WLAN, CDMA 2000, WiMAX, etc.) radioaccess.

The mobile terminal receives or transmits a service request through thefirst access network, and starts initiation of the service by controlsignaling through the first access network. The mobile terminal mayfurther receive a command to activate the mobile terminal's interface tothe second access network for service provision via the first accessnetwork, and may activate its interface to the second access network forcontinuing the initiation of the service or for receiving service datathrough the second access network. In an exemplary embodiment of theinvention, activating the mobile terminal's interface to the secondaccess network is similar to transiting into an active state for thesecond access network by the mobile terminal.

In a further embodiment of the invention, the method suggest to furtherset up a radio connection for service provision between the mobileterminal and the second access network upon activation of the mobileterminal's interface to the second access network. Thereupon, a routingentity in a core network may be informed on setup of the radioconnection.

In another embodiment of the invention the mobile terminal has beenassigned a first IP address for communication through the first accessnetwork and a second IP address for communication through the secondnetwork prior to receiving the service request. The mobile terminal mayuse the first IP address as a care-of address for receiving dataaddressed to the second IP address.

In sleep state, the mobile terminal's interface to the second accessnetwork is deactivated. Alternatively, the mobile terminal periodicallyreceives broadcast system information from the second access networkand/or does not transmit any uplink data to the second access networkwhile in sleep state.

In a further embodiment of the invention, the command to activate themobile terminal's radio interface comprises radio access networkparameters for use by the mobile terminal.

Moreover, the invention provides another embodiment related to methodfor initiating a service for a mobile terminal through a first accessnetwork. In this embodiment, the mobile terminal has IP connectivity toa second access network and is in a sleep state in the first accessnetwork. A network entity in a core network, which could, for example,be an IP mobility management entity, transmits a service initiationrequest through the second access network to the mobile terminal.Alternatively, the service request may be received from the mobileterminal at the network entity.

Thereupon, initiation of the service by control signaling with themobile terminal through the second access network is started. Further,system resources for providing the requested service are established inthe first access network, and the network entity may transmit a commandto the mobile terminal to activate its interface to the first accessnetwork, wherein the command is transmitted through the second accessnetwork.

In another embodiment of the invention, the network entity may receive amessage indicating that the mobile terminal has established a radioconnection to the first access network upon having transmitted theactivation command, and routes service-related data destined to themobile terminal through the first access network upon having receivedthe message.

The advantage of the operation described above is that serviceinitiation may be already started (and possibly even service provision)through the second access network, while resources in the first accessnetwork are being configured and the mobile terminal reactivates itsinterface to the first access network. As soon as the resources forservice provision (and for finishing service initiation) are establishedin the first access network, the distribution path for service relateddata may be switched from the second to the first access network.

In order to provide data to the mobile terminal prior to activating itsinterface to the first access network, another embodiment of theinvention foresees that a care-of address is registered previous toservice initiation by the mobile terminal at an IP mobility managemententity in the core network. This care-of address is used for packettransmissions to the mobile terminal through the second access network.

In a further embodiment of the invention a network entity of the corenetwork may further determine whether to utilize the first or the secondaccess network to provide the requested service to the mobile terminal,and the transmission of the command to activate the interface to thefirst access network and the configuration of system resources areperformed, if it is decided to utilize the first access network.

Another embodiment of the invention foresees that the command toactivate the mobile terminal's radio interface is transmitted by anetwork entity of the core network and comprises radio access networkparameters for use by the mobile terminal. The radio access networkparameters may speed up the setup of a connection to the first accessnetwork upon activating the interface by the mobile terminal.

In a variation of this embodiment, the radio access network parametershave been received by the network entity during configuration of systemresources in the first access network from a mobility management and/oruser plane entity to be serving the mobile terminal in the first accessnetwork.

A further embodiment of the invention foresees that a mobilitymanagement and/or user plane entity to be serving the mobile terminal inservice provision through the first access network is determined.Moreover, in another embodiment of the invention also radio accessparameters of the mobile terminal for service provision through thefirst access network may be determined. The radio access serviceparameters may, for example, include the service radio cell to beserving the mobile terminal in service provision.

In another advantageous embodiment of the invention the configuration ofsystem resources comprises transmitting context information to amobility management and/or user plane entity in the core network servingthe mobile terminal in service provision through the first accessnetwork. For example, this context information may have been buffered ina network entity of the core network having mobility management and/oruser plane entity functionality upon the mobile terminal transiting intosleep state.

In an alternative embodiment of the invention, a command to reactivate acontext is transmitted to the mobility management and/or user planeentity to be serving the mobile terminal.

According to another alternative embodiment of the invention, a mobilitymanagement and/or user plane entity that has been serving the mobileterminal upon transiting into sleep state is instructed to transfer acontext to the mobility management and/or user plane entity to beserving the mobile terminal.

Another embodiment of the invention relates to a method for reducing thepower consumption of a mobile terminal supporting connectivity to atleast two access networks. For example, at least one of these two accessnetworks may be a radio access network, such as a 3GPP-based (e.g.,E-UTRAN, HSPA, UTRAN, etc.) or non-3GPP-based (e.g., WLAN, CDMA 2000,WiMAX, etc.) radio access.

According to the embodiment the mobile terminal attaches to a firstnetwork. Thereby, the mobile terminal obtains an IP address for use incommunication through the first access network. The IP address is thenregistered as a care-of address of the mobile terminal at an IP mobilitymanagement entity that is providing IP mobility management functionalityto the mobile terminal.

Upon having registered the care-of address at the IP mobility managemententity, the mobile terminal may transit into a sleep state forcommunication via a second access network.

In a further embodiment of the invention, the mobile terminal may attachto the second access network. In this attachment procedure, the mobileterminal may obtain an IP address for use in communication through thenetwork. The IP address obtained when attaching to the first accessnetwork may be used as the care-of address, when transiting into sleepstate.

In an exemplary embodiment the mobile terminal deactivates its airinterface to the second access network in sleep state. Alternatively, insleep state, the mobile terminal periodically receives broadcast systeminformation from the second access network and/or does not transmit anyuplink data to the second access network.

In another embodiment of the invention, a tracking area is assigned tothe mobile terminal within the first radio access network. The trackingarea may, for example, allow paging the mobile terminal through thefirst access network.

In a further embodiment of the invention, a network entity in the corenetwork requests context information from a mobility management and/oruser plane entity serving the mobile terminal in the second accessnetwork when transiting into sleep state.

In another embodiment of the invention, context information may bebuffered/stored in the network entity for later use in service provisionto the mobile terminal through the second access network.

An alternative to storing the context in the network entity may be thedeactivation of a context at a mobility management and/or user planeentity in the core network serving the mobile terminal when transitinginto sleep state.

Upon having registered the care-of address for the mobile terminal, itmay be further advantageous to redirect data traffic directed to themobile terminal to a gateway for provision to the mobile terminalthrough the first access network.

According to another embodiment the availability of the mobile terminalis checked through the first access network. For example, the mobilitymanagement entity may check the availability on an event triggered basisor periodically.

Further, in situations where connectivity to the first access network islost or no data is transferred, it may be beneficial to reactivate theinterface to the second access network. Therefore, another embodiment ofthe invention proposed that the mobile terminal activates its interfaceto the second access network in response to a timeout of a timer or ifno data have been received via the interface to the first access networkfor a predetermined time span. Further, upon determining thatconnectivity to the first access network has been lost or no data istransferred, the interface may be (optionally) deactivated.

According to another embodiment of the invention, attaching to the firstaccess network comprises transmitting a message from the mobile terminalto the IP mobility management entity to register the obtained IP addressas the care-of address for an IP address of the mobile terminal to beused for communication through the second access network.

Moreover, one embodiment of the invention further foresee to obtain anIP address to be used by the mobile terminal for communication throughthe second access network when authenticating the mobile terminal in thefirst access network.

In another embodiment of the invention, the mobile terminal may beinformed on an IP address to be used for communication through thesecond access network when attaching to the first access network.

Further, in another embodiment of the invention it is foreseen togenerate a context at a mobility management and/or user plane entitywithin a core network connected to the first and second access network.

Alternatively, a mobility management and/or user plane entity within acore network connected to the first and second access network may beinstructed by the IP mobility management entity to generate a context .

Further, when authenticating the mobile terminal in the first accessnetwork an identification of the IP mobility management entity may beobtained according to another embodiment of the invention.

In the embodiments described herein, the first and the second accessnetwork may use different access technologies.

Another embodiment of the invention is related to a mobile terminalcapable of communicating via at least a first and second access networkand having IP connectivity to the first access network and is in a sleepstate in the second access network. The mobile terminal comprises atransceiver for receiving or transmitting a service request through thefirst access network, and for starting initiation of the service bycontrol signaling through the first access network. The transceiver maybe further operated to receive a command to activate the mobileterminal's interface to the second access network for service provisionvia the first access network. Further, the mobile terminal may comprisea controlling unit for activating the mobile terminal' interface to thesecond access network for continuing the initiation of the service orfor receiving service data through the second access network.

Another embodiment of the invention relates to a network comprising atleast one network element that can be operated to participate in themethod according to one of the various embodiments described herein.

Another embodiment of the invention provides a further mobile terminalthat is supporting connectivity to at least two access networks. Themobile terminal comprises a transceiver for attaching the mobileterminal to a first network, thereby obtaining an IP address for themobile terminal for use in communication through the first accessnetwork, and for registering the IP address as a care-of address of themobile terminal at an IP mobility management entity, wherein the IPmobility management entity provides IP mobility management functionalityto the mobile terminal. Further the terminal includes a processor fortransiting into a sleep state for communication via the second accessnetwork upon having registered the care-of address at the IP mobilitymanagement entity.

In another embodiment of the invention the mobile terminal is furtheroperated to perform the steps of the method according to one of thevarious embodiments described herein.

BRIEF DESCRIPTION OF THE FIGURES

In the following the invention is described in more detail in referenceto the attached figures and drawings. Similar or corresponding detailsin the figures are marked with the same reference numerals.

FIGS. 1 & 2 show examples of evolved 3GPP architectures,

FIG. 3 shows another exemplary 3GPP architecture according to anotherembodiment of the invention where different functional entities arecombined in Inter AS anchors,

FIG. 4 shows the different states a mobile terminal may be in and thepossible transitions from one state to the other according to anembodiment of the invention,

FIG. 5 shows an exemplary flowchart of a mobile terminal transiting intosleep state according to an exemplary embodiment of the invention,

FIG. 6 shows an exemplary flowchart of the operations performed by themobile terminal and the core network when initiating a service to themobile in sleep state according to an embodiment of the invention,

FIG. 7 shows other exemplary flowchart of the operations performed bythe mobile terminal and the core network when transiting the mobileterminal into sleep state according to an embodiment of the invention,

FIG. 8 shows an exemplary signaling procedure for attaching a mobileterminal to a 3GPP-based access network according to an exemplaryembodiment of the invention,

FIG. 9 shows an exemplary signaling procedure for attaching a mobileterminal to a non-3GPP-based access network according to an exemplaryembodiment of the invention,

FIG. 10 shows an exemplary signaling procedure for transiting a mobileterminal from active state to idle state according to an exemplaryembodiment of the invention,

FIG. 11 shows an exemplary signaling procedure for transiting a mobileterminal from idle state to sleep state according to an exemplaryembodiment of the invention,

FIG. 12 shows an exemplary signaling procedure for initiating a serviceto a mobile terminal in sleep state according to an exemplary embodimentof the invention, and

FIG. 13 shows an exemplary overview of the sequence signaling proceduresas shown in FIGS. 8 to 12.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the invention is the introduction of a sleep state. Amobile terminal capable of communicating/accessing two access networksmay be transited into sleep state for one of the access networks toreduce power consumption, while the terminal maintains connected via theother access network. Obviously, it is advantageous to enter into sleepstate only if no services are currently running through the accessnetwork for which the mobile terminal wants to transit to sleep state orif running services may be redirected through the other access network.

Another aspect of the invention is to speed up service initiation for aservice to be provided to the mobile terminal through the access networkfor which the mobile terminal is in sleep state. For this purpose,system resources are configured in the access network for which themobile terminal is in sleep state while service initiation is alreadystarted through the other access network.

The principles outlined herein may also be advantageously used inheterogeneous networks, as, for example, outlined in the technicalbackground section above.

To facilitate the establishment of system resources for the service anembodiment of the invention foresees that context information of theaccess network for which the mobile terminal is in sleep state may bemaintained for the mobile terminal in the network even in sleep state.Upon service activation, the context information may be advantageouslyused to establish the system resources for the service. As soon as theresources are established (i.e., the mobile terminal enters active statefor the access network through which the service is to be provided), thedistribution path for service data and service related signaling may beswitched to route the packets through the now activated access networkto the mobile terminal.

The context information depends on the core network entity. For example,a context in a mobility management entity may, for example, comprisemobility states, authentication information, ciphering information,temporary IDs assigned to the mobile terminal for use in the accessnetwork for which the mobile terminal is in sleep state, QoS relatedinformation, etc. When establishing a context in the user plane entity,the context may, for example, comprise parameters of the IP bearerservice or network internal routing information.

The different embodiments of the invention may be implemented in asystem architecture as shown in FIGS. 1 and 2. It should be noted thatherein the term “entity” denotes a functional unit within the radioaccess network or core network. Hence, it is possible that several ofthese functional entities are combined in a single (physical) networkelement. In this respect, FIG. 3 shows another exemplary 3GPParchitecture according to another embodiment of the invention wheredifferent functional entities are combined in Inter AS anchors.

Further, a mobility management entity (MME) denotes a functional entitymanaging mobility of terminal according to the protocols used in arespective access network (and core network - depending on thearchitecture) that is served by the mobility management entity.Similarly, an IP mobility management entity denotes an entity supportingIP mobility. Examples of IP mobility management entities are thefunctional entities specified in the Mobile IPv6 or Mobile IPv4 protocolthat are commonly referred to as the “home agent” and “foreign agent”.

It should be understood that in the context of this invention a mobileterminal is a terminal that may be connected to various networks as theuser of the terminal moves. Hence, the term “mobile” is not intended tolimit to the invention to its use in combination with technologieshaving a radio/air interface.

FIG. 4 shows the different states a mobile terminal may be in and thepossible transitions from one state to the other according to anembodiment of the invention. The definitions of the active state, idlestate and detached state are similar to those described in the technicalbackground section. The sleep state suggested by the invention is a newstate which enables reducing power consumption of the terminal whileallowing fast service activation as will be explained herein.

In one embodiment the sleep state is defined as a state where the mobileterminal deactivates its interface to an access network. A mobileterminal being in sleep state in an access network means that the mobileterminal has deactivated its interface to this access network. Ifcompletely deactivating the interface, the mobile terminal receives andtransmits no data through this interface, which is thus the potentiallymost efficient form of saving power in sleep state.

Another alternative definition of the sleep state is that the mobileterminal does not completely deactivate the interface to a particularaccess network but activates the interface, for example, periodically toreceive system broadcast information from the network. However, nouplink data is transmitted by the mobile terminal through the accessnetwork for which it is in sleep state.

FIG. 5 shows an exemplary flowchart of a mobile terminal transiting intosleep state according to an exemplary embodiment of the invention.First, the mobile terminal is attached 501, 502 to a first and a secondaccess network, or attaches thereto. When attaching to the accessnetworks, the mobile terminal selects or is assigned an IP address thatit is using for communication through a respective one of the accessnetworks.

For example, the first access network may be the home network of themobile terminal (e.g., an 3GPP network). When using Mobile IPterminology, IP address #1 can also be referred to as the home address(HoA) of the mobile terminal in its home network according to thisexample.

The second access network could be, for example, wireless or wirednon-3GPP access network, such as a WLAN access network or a (A)DSLnetwork that the user of the terminal utilizes at home, at a hotspot, atan airport, hotel, etc. The second IP address #2 may be thus an IPaddress assigned to the mobile terminal for use in communication throughthe second access network. When using Mobile IP terminology again, thesecond access network may also be referred to as a visited network andthe network may comprise a foreign agent to support IP-layer mobility.

Upon having decided or having been instructed to transit to a sleepstate for the first access network, the mobile terminal registers 503its IP address #2 of the second (visited) network as its care-of addressat an IP mobility management entity located in a core network connectedto the first and second access network. In a variation, thisregistration of a care-of address will also result in a rerouting ofdata directed to the mobile terminal's IP address #1 through the secondaccess network.

Having received a confirmation for the registration of the care-ofaddress, the mobile terminal may enter 504 into sleep state.

Further, in another embodiment the attachment to the first accessnetwork has also established context information within the individualnetwork entities of the first access network. According to thisembodiment, this context information may be preserved by buffering theircontent within the network so as to speed up service setup through thefirst access network when receiving a service request requiring datatransport through the first access network, e.g., due to the service'sQoS requirements.

In order to preserve the context information on the mobile terminal's IPconnectivity in the first access network, the context may be transferredto a mobility management and/or user plane entity serving the mobileterminal. In this case the network entities having maintained thecontext information in the first access network (and core network) maydelete the context information.

The removal of context information in the network entity/entitiesserving the mobile terminal in communication through the first accessnetwork may be advantageous, as malfunctioning of paging the mobileterminal can be avoided. Typically, in case a network entity (forexample, a mobility management and/or user plane entity) maintains acontext for a mobile terminal (for example, in idle state), it alsoassumes that the mobile terminal may be paged through its network (thefirst access network). However, in sleep state the mobile terminal mayhave deactivated its interface to the first access network, so thatpaging is no longer possible. To resolve this situation, the transfer ofthe context to another mobility management and/or user plane entityserving the mobile terminal may be beneficial.

An alternative solution could be an enhancement of the networkentity/entities serving the mobile terminal in the first access network.In this case, the network entity/entities may maintain the contextinformation but will reroute paging requests through the second accessnetwork as long as the mobile terminal is in sleep state for the firstaccess network.

FIG. 6 shows an exemplary flowchart of the operations performed by themobile terminal and the core network when initiating a service to themobile in sleep state according to an embodiment of the invention,

In this example, it is assumed that the mobile terminal is 601 in sleepstate for access network #1 while maintaining connectivity throughaccess network #2. Generally, a service request may be received 611 at aresponsible network entity in the core network from the mobile terminalor from another requesting user or entity. Steps 602 and 612 are thusonly performed, if the mobile terminal is not initiating the service.

In this example, the network entity informs the mobile terminal on therequested service by sending 612 a service initiation request to themobile terminal through the second access network (access network #2).The mobile terminal received 602 the service initiation request, and maystart 603, 613 service initiation through access network #2. Forexample, the service may be initiated by SIP signaling as specified inIETF RFC 3261, “SIP: Session Initiation Protocol”, incorporated hereinby reference (available at http://www.ietf.org) or any other signalingprotocol allowing to setup an application layer service.

Further, it may be decided 614 within the core network, whether theservice constraints require the use of the first access network forservice provision or not. For exemplary purposes it is assumed that dueto QoS constraints associated to the service, the first access network(access network #1) is to be used for the service. Therefore, as a nextstep the resources for service provision are established 615 in thefirst access network (and also in the core network, if required).

When, for example, assuming an architecture as shown in FIG. 1 and thatan IMS service is to be provided to the mobile terminal, the networkconfigures all necessary resources along the distribution path (e.g.,Inter AS anchor 102→UPE 104→(enhanced) NodeB) in the wired part of thenetwork by establishing the appropriate contexts within the network.

Upon having finished resource reservation, the mobile terminal isinstructed 616 to activate its interface to access network #1, i.e., totransit to active state. This command may, for example, also include RANparameters that allow the mobile terminal to establish a connection tothe access network #1 faster than using the access network-specificprocedures for transiting into active state. For example, the RANparameters may include at least one of a scrambling code, frequencyinformation, power control information, depending on the type of theradio access.

Upon reception of the activation command 604 at the mobile terminal,same will activate 605 the interface to access network #1. Thisactivation may, for example, include the establishment of the servicebearer(s) required for communicating service related user plane andcontrol plane data through access network #1.

In a variation of the embodiment outlined with respect to FIG. 6, it isassumed that mobile terminal related context information have beenpreserved in the network while the mobile terminal has been in sleepstate as explained above. The setup of service resources in accessnetwork #1 may be speed up when communicating the buffered contextinformation to the relevant network entities along the distribution pathtowards the mobile terminal through access network #1.

For example, assuming that Inter AS anchor 102 in FIG. 1 has MME/UPEfunctionality and has preserved the context information it may providethe context information to MME 103 and UPE 104 when establishing thesystem resources. Similarly, the MME 103 and/or UPE 104 may forwardrelevant context information to the downstream entities in accessnetwork #1.

As the mobile terminal may have moved and may no longer be served by the“old” MME/UPE, the Inter AS anchor 102 may determine which new MME/UPEis now serving the mobile terminal. Accordingly, the context informationwill be provided to the determined MME/UPE. If, for example, the “old”MME/UPE preserved the context, the Inter AS anchor 102 may instruct the“old” MME/UPE to forward the context information to the new MME/UPE. Ifthe “old” MME/UPE is also now serving the mobile terminal, it may beinstructed to reactivate the context, i.e., set the mobile terminalstatus back to active state.

Another alternative embodiment of the invention provides a solutionwhere the initial attachment of the mobile terminal to access network #1is not necessary. FIG. 7 shows other exemplary flowchart of theoperations performed by the mobile terminal and the core networkaccording to this embodiment of the invention when transiting the mobileterminal into sleep state. The terminal first attaches 701 to accessnetwork #2 and obtains an IP address #2 assigned 711 to it by theresponsible network entity of access network #2 (or the core network).Upon having attached to access network #2, the mobile terminal performsauthentication 702, 712 with the access network #2.

In an advantageous variation of this embodiment, the mobile terminalprovides information to the participating network entity in accessnetwork #2 in the authentication signaling such that the network entitymay identify the home network (access network #1/core network) of themobile terminal. This could allow the network entity to identify the IPmobility management entity of the home network and optionally to obtainan IP address #1 (home address) for the mobile terminal on behalf ofsame.

Alternatively, the mobile terminal may directly identify the IP mobilitymanagement entity in the authentication signaling and/or may choose anIP address to utilize for communication with its home network.

In any case, the mobile terminal may proceed and register 703 the IPaddress for access network #2 as its care-of address at the IP mobilitymanagement entity in its home network. The registration of the care-ofaddress may alternatively performed 713 by the network entity in accessnetwork #2 authenticating the mobile terminal. Upon registration of thecare-of address, the mobile terminal may enter into sleep state for itshome network (access network #1). It should be noted that the home agentof the mobile terminal does not have to be located in the core networkattached to access network #1 and #2. If, for example, both accessnetworks are visited networks, the request for registration of thecare-of address is provided to the mobile terminal's home agent in itshome network.

As no attachment to access network #1 (home network) has been performed,no context information for the mobile terminal for communication throughaccess network #1 is available. To speed up the setup of a service to beprovided through access network #1, the IP mobility management entity inthe home network (core network) will generate or initiate the generationof context information for later resources reservation. Upon serviceinitiation this context information may be provided to the networkentity/network entities along the distribution path in access network#1, as has been explained with respect to FIG. 6 above.

In the following, details of the procedure for fast service activationof a multimode UE with reduced power consumption according to differentembodiments of the invention are described. It should be noted that inthese example, it is assumed that a first access network for which themobile terminal may enter sleep state is a 3GPP enabled network, whilethe second access network is a non-3GPP enabled network. However, theprinciples outlined in the following would not be limited to being onlyapplicable to this exemplary scenario.

FIG. 13 shows high level signaling of the procedure and gives anoverview of the sequence signaling procedures as shown in FIGS. 8 to 12.The mobile terminal is referred to as a User Equipment (UE). As the UEis capable of communicating with 3GPP enabled and non-3GPP enablednetworks in this example, it is also referred to as a multimode UE.

According to an exemplary embodiment of the invention, the UE firstattaches to the 3GPP Radio Access Network (RAN), and subsequentlydiscovers and selects a non-3GPP RAN. Further, the UE establishes aconnection to the non-3GPP RAN.

Next, the UE goes to idle state with the 3GPP radio interface.Subsequently, the UE's transiting into sleep state is initiated tofurther reduce power consumption. Then a new service request is incomingfor the 3GPP interface, and in the following the fast transition fromthe sleep state to active state is performed.

The steps briefly explained above will be elaborated on in the followingreferring to the exemplary procedures shown in FIGS. 8 to 12.

FIG. 8 shows an exemplary signaling procedure for attaching a mobileterminal to a 3GPP-based access network according to an exemplaryembodiment of the invention.

Upon the UE having discovered and selected the 3GPP Access System instep 1, for example, after power on, the UE attaches to the 3GPPnetwork. This is done by sending an attach request to the 3GPP networkin step 2, which may, for example, include an old temporary ID of the UEpreviously used in the network or alternatively an permanent ID of theUE, e.g., the IMSI. Further, the UE may suggest a preferred IP addressfor use in the request.

The MME/UPE receiving the request may subsequently (step 3) allocatetemporary IDs to the UE. In addition, the last registered Tracking Area(TA) of the UE is stored in the MME/UPE (i.e., network element providingMME and/or UPE functionality). Subsequently the UE may be authenticated(step 4) in the network and the MME registers at the AAA/HSS server(step 5). Upon the UE and the Network (MME/UPE) are mutuallyauthenticated and the MME/UPE having registered as serving the UE at theHSS/AAA, the HSS/AAA confirms the registration (step 6), and transferssubscription data, and policy and charging control information to theMME/UPE. This information may, for example, be maintained in a UErelated context within MME/UPE.

Next, an Inter AS Anchor is selected (step 7). This may, for example, bedone by the MME/UPE based on information transferred in an attachrequest from the UE. In this process the IP address to be used by the UEfor IP-based communication through the 3GPP network is determined.

In step 8, the Default IP Access Bearer QoS may be configured and instep 9 the UE is informed on its IP address. Typically, assuming thatthe 3GPP network is the UE's home network, this IP address is the IPHome Address (HoA) of the UE. Otherwise the assigned IP address is acare-of address CoA that would have to be registered at the UE's homeagent (HA) in the UE's home network.

Upon having received a confirmation of the UE's attachment (step 10) theUser Plane route between eNodeB and MME/UPE and also the route (path)between MME/UPE and Inter AS Anchor is updated (step 11). This may, forexample, be realized by Binding Update / Binding Acknowledgementmessages. Then, user plane traffic can be transferred to the UE (step12).

FIG. 9 shows an exemplary signaling procedure for attaching a mobileterminal to a non-3GPP-based access network according to an exemplaryembodiment of the invention. Upon having attached to the 3GPP network,the UE may select (step 1) a non-3GPP Access System, for example, a WLANAccess Network.

Then, a local IP address is assigned to the UE, either by a gateway(e.g., the PDG -Packet Data Gateway) or by other means. If the gatewayassigns the address, it may, for example, interrogate the user's HomeAAA server to authenticate/authorize the user. In this communication,the gateway may receive the Inter AS Anchor IP address and the UE's HoAand may inform the UE about the Inter AS Anchor IP address and the UE'sHoA.

After the UE is authenticated/authorized (step 3) at the gateway, the UEor the gateway sends (step 4) a Location Update (e.g., Binding Update ofMIPv6—see IETF RFC 3775, “Mobility Support in IPv6”, incorporated hereinby reference, available at http://www.ietf.org) to the Inter AS Anchor.The Location Update may also comprise additional location informationapart from an IP address. The Location Update may also comprise filterrules about the services or flows that should be transferred to the UEover the non-3GPP Access System. Alternatively, the filter rules may berequested from a PCRF or additional rules are transferred from the PCRFto the Inter AS Anchor.

Then, the Inter AS Anchor authenticates (step 5) the UE and replies withan Acknowledgement (MIPv6 Binding Update Acknowledge) (step 6).

FIG. 10 shows an exemplary signaling procedure for transiting a mobileterminal from active state to idle state according to an exemplaryembodiment of the invention. In case the UE is not using the 3GPP AccessSystem (step 1), i.e., no user data packets are transferred, the MME/UPEor the eNodeB may trigger (step 2) the UE to go to idle state. In thisstate the mapping between temporary and permanent user IDs and the lastregistered TA is stored in the MME/UPE. When the UE moves to anothercell and changes the TA, it may perform TA registration procedure (step3), i.e., a connection with the 3GPP Access System is established andthe new TA is signaled to the MME/UPE.

FIG. 11 shows an exemplary signaling procedure for transiting a mobileterminal from idle state to sleep state according to an exemplaryembodiment of the invention. For exemplary purposes, a network as shownin FIG. 2 is assumed to explain the operations of the UE and networkwhen transiting the UE from idle state to sleep state.

Since the UE has an active non-3GPP connection established and the 3GPPAccess System is not used (idle state), the UE or the network may decide(step 1) to further reduce the power consumption and the signaling loadon the radio link and in the network. The decision can be made, forexample, based on an expired timer that has been started upon the UEentering idle state.

For entering the sleep state, the UE sends (step 2) a message to theInter AS Anchor 2 (e.g., a MIPv6 Binding Update, including a temp ID andthe old MME/UPE) to trigger Inter AS Anchor 2 to register itself as newnon-3GPP AS MME/UPE for the UE in sleep state. In this example, it isalso assumed that Inter AS Anchor 2 (non-3GPP AS Anchor) provides MMEand UPE functions (non-3GPP AS MME/UPE). It is also possible, that thenon-3GPP Inter AS Anchor 2's MME/UPE functions are logically separatedfrom the Inter AS Anchor in another network entity/other networkentities.

In order to differentiate the 3GPP Access System registration from thenon-3GPP Access System registration in the new non-3GPP AS MME/UPE, theInter AS Anchor may allocate (step 3) a special TA for the non-3GPPAccess System, which is e.g., stored in the non-3GPP AS MME/UPE.

According to one exemplary implementation, the non-3GPP AS Anchor's MMEfunction may send (step 4) the temp ID of the UE to the old networkentity with MME/UPE function that has been serving the UE so far. Theold MME/UPE may respond by sending (step 5) the UE's context (including,e.g., the permanent user ID, security and IP connectivity parameters) tothe new non-3GPP AS MME/UPE. The temporary ID of the UE provided in step4 is thereby used to identify the UE and context.

In an alternative implementation, the non-3GPP AS MME/UPE may commandthe old 3GPP AS MME/UPE to preserve the context information for the UE.In this implementation, the 3GPP AS MME/UPE would indicate the sleepstate in the UE context and may update the User Plane route to pass alldata directed to the UE through non-3GPP AS Anchor 2. Further, the 3GPPAS MME/UPE may indicate in their UE context that the UE can no longer becontacted (e.g., paged) through the 3GPP network, so that all servicerequests need to be redirected through the non-3GPP network.

The Inter AS Anchor further triggers the non-3GPP AS MME/UPE to registeritself as new MME/UPE for the UE in idle state. In step 6, the non-3GPPAS MME/UPE sends a registration message to the HSS which will confirm(step 7) the registration. Further, Inter AS Anchor 2 confirms (step 8)the registration with the UE (e.g., with a MIPv6 Binding UpdateAcknowledgment). Upon receiving the confirmation, the UE may enter intosleep state (step 10).

In case the UE was connected to multiple Inter AS Anchors and it isrequired that these anchors keep located on the user plane path, thepath between these Inter AS Anchors and the Inter AS Anchor serving thenon-3GPP connection is updated (step 9).

Because the connection over the non-3GPP Access System is unreliable,the Inter AS Anchor 2 may optionally check (step 11) the reachability ofthe UE, e.g., with periodically sending MIPv6 Binding Refresh Requestmessages, which must be answered by the UE with Binding Update. If theUE is not reachable over the non-3GPP interface anymore (e.g., becauseit has moved out of WLAN coverage—which could e.g., be detected by theUE not answering a given number of consecutive Binding Refresh Requestmessages), Inter AS Anchor 2 triggers the transition back to idle statein the 3GPP network. Also, if the UE does not receive reachabilitymessages anymore for some time, it may reactivate its 3GPP interface andtransits back to 3GPP idle state.

FIG. 12 shows an exemplary signaling procedure for initiating a serviceto a mobile terminal in sleep state according to an exemplary embodimentof the invention. In case a call/service (e.g., IMS or MBMS - see, forexample, 3GPP TS 23.246, “Multimedia Broadcast/Multicast Service (MBMS);Architecture and functional description”, V. 6.9.0, incorporated hereinby reference, available at http://www.3gpp.org) only receivable over the3GPP Access System is incoming or is initiated by the UE in sleep state(step 1), Inter AS Anchor 2 may detect this based on pre-establishedfilter rules (e.g., SIP request is detected—see IETF RFC 3261) andstarts the transition to 3GPP active state for the UE. Only receivablevia the 3GPP Access System may, for example, mean that the non-3GPP ASis not capable of providing the service at all, not atrequested/required QoS parameters associated to the service, UE policyand billing rules or AAA constraints require the provision through the3GPP network.

In case of an incoming call/service, the Inter AS Anchor 2 forwards ortunnels the call/service signaling for initiating the call/service tothe UE through the non-3GPP Access System (step 2). Regardless ofwhether it is an incoming or UE-initiated call/service, the UE beginswith the service establishment using the non-3GPP Access Systemconnection.

At the same time the non-3GPP AS MME/UPE functionality of Inter ASAnchor 2 may select (step 3) new network entities with MME/UPEfunctionality (new MME/UPE) to be serving the RAN nodes the UE is goingto use. This could, for example, be accomplished by mapping availablenon-3GPP AS location information (e.g., derived from the topologicallycorrect IP address assigned to UE's non-3GPP network interface) to thecorrespondent TA and RAN nodes in the 3GPP AS. In this latter case, thenon-3GPP AS may be a stationary access system (e.g., ADSL connection).

Alternatively, if the 3GPP cell coverage is larger than the coverage ofthe non-3GPP AS (WLAN hotspot), the NodeB serving the UE may probably bethe same than before switching to the non-3GPP AS. If no locationinformation mapping is possible, the non-3GPP AS MME/UPE may select adefault MME/UPE serving all RAN nodes in the network for the purpose offast 3GPP activation of multimode UEs in sleep state. In this case,after the 3GPP radio connection is established, the default MME/UPE canhandover the UE to a better MME/UPE (i.e., closer to the UE).

Furthermore, the non-3GPP AS MME/UPE triggers (step 4) the new MME/UPEto setup resources for the call/service. The new MME/UPE sends (step 5)a resource preparation request to the relevant nodes, e.g., the NodeB,in case information about the corresponding RAN nodes is available.Alternatively the non-3GPP AS MME/UPE or Inter AS Anchor 2 triggers theother involved Inter AS Anchors to setup resources.

The eNodeB and the MME/UPE confirm (steps 6 and 7) the resourcepreparation to the non-3GPP AS MME/UPE (including, e.g., IP addressassigned by MME/UPE, preferred TA and other parameters). In response tothe confirmation, Inter AS Anchor 2 sends (step 8) a 3GPP radioactivation command message to the UE to instruct the UE to transit fromsleep state to active state. E.g., this activation command may beincluded in a MIPv6 Binding Refresh Request with the IP address assignedby the new MME/UPE, preferred TA, serving cell and other parameters)that is transmitted to the UE via the non-3GPP access network. Inresponse to the command, the UE activates the 3GPP radio interface andestablishes synchronization with the 3GPP Radio Access Network and the3GPP connection for service delivery (step 9). The RAN node (e.g.,eNodeB) may send (step 10) an activation complete message to the newMME/UPE and the new MME/UPE indicates (step 11) the completion of the3GPP radio connection setup to the non-3GPP AS MME/UPE.

Next, the user plane between UE, new UPE and Inter AS Anchor 1 (or InterAS Anchors, when multiple are involved) is updated (step 12). This maytypically include the update to the user plane route (compare step 9 inFIG. 11, where the user plane has been redirected through the non-3GPPaccess network). Finally, the new MME may update (step 13) the locationwith the HSS/AAA that confirms (step 14) the registration. Optionally,the HSS/AAA may inform the non-3GPP MME/UPE that the UE context may bedeleted.

The contents of the messages exchanged during resource setup in steps 4to 7 may depend on the strategy used to preserve the UE context in 3GPPsleep state. If the context has been transferred to the non-3GPP MME/UPEas suggested in FIG. 11, the resource preparation request in step 4 mayinclude the context information to aid the new MME setting up theresources.

If preserving the UE context in the MME/UPE that has been serving the UEbefore transiting to sleep state (old MME/UPE), operation will depend onwhether this old MME/UPE is still serving the UE when receiving thecall/service. If so, the old and new MME/UPE may simply reactivate thecontext upon receiving the resource preparation request. Further, it mayalso update the user plane route.

If the new MME/UPE does not correspond to the old MME/UPE; the non-3GPPMME/UPE may instruct the old MME/UPE to initiate resource establishmentfor the service. The old MME/UPE may then instruct the new MME/UPE tosetup the resources and may include the preserved context information tothe request.

Another optional implementation detail is a trigger for transiting fromsleep state to idle state by the UE. When the UE is inactive over thenon-3GPP Access System connection for some time (e.g., detected bytime-out), the network or the UE may decide to transit back to idlestate in the 3GPP AS, i.e., the UE will (re)activate its air interfaceto the 3GPP AS. The UE may also deactivate the non-3GPP radio interfaceto save power. The UE may perform a TA update, which results in the UEcontext information being transferred from the non-3GPP AS MME/UPE tothe new MME/UPE serving the UE in the 3GPP AS.

The advantage of moving back to idle mode is that the power consumptionof an inactive, but activated non-3GPP Access System connection can benoticeable higher than the power consumption of a 3GPP interface in idlestate.

In some previous embodiments of the invention, it has been assumed thatnon-3GPP AS MME/UPE and Inter AS Anchor are separated so that signalingbetween the entities has been required. In another embodiment of theinvention, instead of using a separate non-3GPP AS MME/UPE, also the oldMME/UPE can be used to store the sleep state as indicated above. In caseof an incoming call/service, the old MME/UPE detects based on the sleepstate that non-3GPP Access System connection is active and thus forwardsthe packets to the Inter AS Anchor serving the non-3GPP Access Systemconnection.

Further, it has also been assumed in some embodiments of the inventionthat the 3GPP radio interface of the multimode UE in sleep state isswitched off. In another embodiment of the invention the UE does notswitch off the 3GPP radio interface completely. According to thisembodiment the UE may listen periodically to broadcast systeminformation and only stops sending messages over the 3GPP radiointerface, e.g., no location updates are sent over the 3GPP radiointerface when moving. Instead, location changes of the 3GPP radiointerface (e.g., TA changes or even cell changes) are signaled over theactive non-3GPP Access System connection. This reduces the powerconsumption of the multimode UE, because no 3GPP radio connection mustbe established specifically for location updates and also the amount ofsignaling in the 3GPP network is reduced. This procedure has theadditional advantage that it is possible to have fast service activationand reduced power consumption even when the topological location of thenon-3GPP network interface cannot be used to derive the topologicallocation of the 3GPP network interface.

In some embodiments of the invention it has been assumed that themultimode UE attaches to the 3GPP Access Network using a 3GPP radioconnection. In another embodiment of the invention the UE is attachingto the 3GPP Access Network using the non-3GPP Access Network connection.First the UE attaches to the non-3GPP Access Network, it is providedwith a local IP address and additionally—e.g., during authentication theUE—with a home IP address. After registration of the local IP address asthe care-of address, the UE or the network may trigger the Inter ASAnchor to establish context information for the UE in the non-3GPP ASMME/UPE and to set the mobility state to sleep. Furthermore, the UE mayconnect to other anchors providing connectivity to other services usingthe non-3GPP Access Network connection and the non-3GPP AS MME/UPE asMME/UPE. Then, the UE can receive services via the 3GPP Access Networkand transit from sleep to active.

In previous embodiments of the invention it has been assumed that theInter AS Anchor of the multimode UE providing non-3GPP AS MME/UPEfunctionality is in the home network of the UE and is connected to both,the 3GPP Access Network and to the non-3GPP Access Network. In anotherembodiment of the invention the Inter AS Anchor is in a visited network.The visited network has a connection to one Access Network (e.g., thenon-3GPP Access Network) and another network (e.g., the home network)has a connection to the other Access Network (e.g., the 3GPP AccessNetwork).

Another embodiment of the invention relates to the implementation of theabove described various embodiments using hardware and software. It isrecognized that the various embodiments of the invention may beimplemented or performed using computing devices (processors). Computingdevices or processors may, for example, be general purpose processors,digital signal processors (DSP), application specific integratedcircuits (ASIC), field programmable gate arrays (FPGA) or otherprogrammable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example, RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

1. A system, comprising: a mobile terminal capable of communicating witha core network via a first or second access network; and a base stationin the second access network capable of communicating with the mobileterminal, wherein radio access technology of the first access network isdifferent from radio access technology of the second access network,wherein the mobile terminal includes: a receiver, which, in operation,receives a paging request, which is addressed to the mobile terminal tobe routed through the first access network but is rerouted through thesecond access network when the mobile terminal is attached to the secondaccess network; a transmitter, which, in operation, transmits a messagethrough the second access network in response to the paging request, themessage requesting a service to be delivered through the first accessnetwork; wherein the receiver, which, in operation, receives a handovercommand through the second access network, the handover commanddirecting handover to the first access network; and control circuitry,which, in operation, connects to the first access network based on thehandover command; and wherein the base station includes: a transmitter,which, in operation, forwards the paging request to the mobile terminal,and transmits the handover command through the second access network tothe mobile terminal; and a receiver, which, in operation, receives themessage from the mobile terminal through the second access network inresponse to the paging request.
 2. The system according to claim 1,wherein the control circuitry of the mobile terminal, in operation,informs an entity in the core network that the mobile terminal isconfigured to use the second access network for receiving data when themobile terminal is attached to the second access network.
 3. The systemaccording to claim 2, wherein the entity comprises a mobility managemententity.
 4. The system according to claim 1, wherein the servicecomprises a voice service.
 5. The system according to claim 1, whereinthe mobile terminal is in a deactivated state in the first accessnetwork when the mobile terminal is attached to the second accessnetwork.
 6. The system according to claim 1, wherein a distribution pathfor the service is switched to the first access network after the mobileterminal enters an active state in the first access network.
 7. Thesystem according to claim 1, wherein the message transmitted from themobile terminal through the second access network in response to thepaging request requests initiation of the service.
 8. The systemaccording to claim 1, wherein the handover command is for instructingthe mobile terminal to be activated in the first access network.
 9. Thesystem according to claim 8, wherein the activation in the first accessnetwork includes establishment of a bearer service through the firstaccess network.